Wide-band antenna



Sept. 25, 1951 J. T. BOLLJAHN WIDE-BAND ANTENNA Filed Nov. 13, 1945TRANSMITTER JOHN T. BOLLJAHN Patented Sept. 25, 1951 WmE B N man John T.Bolljahn, Washington, 1)."0." Application masher. 13, 1945, Serial No.628,339 10 Claims. (or'zali-gae) l (Granted under the act ofMarch-3,,1883, as amended 30, 1928; 370 G. 757),

.-..Thi invention relates. to antennas and, moreparticularly,:to-wide-band antennas.

An object of theinvention is to provide an antenna capable of eincientoperation over a wide band of frequencies.

,Another object of the invention isto provide arwide-band antennasuitable for mounting on the exterior surface of a high-speed aircraft.-

A further object of the invention is to provide alwide-i-band antennawhich has a low resistance to the flow-of air at high velocity. ,7The,iradiating element of an antenna in. accordance with the inventioncomprises a. thin sheet of conductive material, which projects through.an opening in an extended conductive surface. Means, which ma comprisea pair of, tapered conductors, are provided for coupling the radiatingelement to a transmission. line. The other end of the line maybeconnected to a Wave signal translator, suchas a radio receiver ortransmitter. Inductive stubs conductively'attached tothe radiatingelement are provided for neutralizing the normal reactance of theradiating element, thereby providing a substantiallynon-reactive-termination at the antenna end of the-transmission line. 3

Other objects, features and advantagesof the invention will be apparentfrom consideration of thefollowing description and the accompanyingdrawing, inwhich Fig. 1 is an elevation view of an exemplary embodimentof the invention, and y Fig. 2 is a sectional view of the, embodimentshown in.,Fig. 1, taken in the plane. 2-2.

Referring now to the drawing, the, radiatingelement of an antennaaccording to the invention may comprise a thin conductive sheetll. Meanscomprising tapered conductors I3, l5- are provided for, efiecting agradual dimensional transition between the radiating element H and acoaxial transmission line H. A pair of inductive stubs comprisingconductive sheets l9, 2| are positioned on each side of the radiatingelement H and are conductively connected thereto between the endsthereof by the shorting bars 23, 25.

The outer tapered conductor I 5 is connected at the wide end thereof toan extended conductive surface 21. The inner tapered conductor [3 may.bea continuation of the radiating sheet element H projecting below theconductive surface 21, .the width of the sheet being tapered down to thediameterof the inner conductor of theline H at the junctiontherebetween. If, as is shown, the thickness of the radiating element IIis substantially the same as the diameter of theinner conductor of theline H, the thickness of conductor I3 need not be tapered.

The conductive surface 21 may comprise, for example, the metallic outersurface of an airrection of air flow. It has been found that minimumwind drag of the antenna is obtained on highspeed aircraft when theratio of width to thicknessof. the antenna is aslarge as is practicable.Consequently, the invention provides an antenna which is well adaptedfor use on high speed aircraft.

I The antenna structure projecting above, the conductive surfaceZ'l:may, be enclosedin a dielectric housing 29 of appropriate dimensions toprotect and strengthen the structure.

The height of the radiating element H above the conductive surface, 21is preferably of the orderof one-quarterwavelength near the center ofthe frequency band over which wide-band operation is desired, The widthof element ll may be of ,the order of one-eighth wavelength.

The tapered conductors efiect a smooth dimensional transition betweentheline I! andthe ane tenna. When the antenna has the dimensions mentionedabove, the impedance .of the antenna provides a satisfactory terminationfor a -ohm transmission line; Consequently, if line, H has acharacteristic impedance of 50 ohms, the tapered conductor sections l3,I5 are designed to maintain a 50 ohm characteristic impedance throughouttheir length between the line H and the radiating element H. However,the tapered conductors may constitute an impedance transformer if thedesired line impedance is not matched .satisfactorilyby. the, antennaimpedance. I

.While a radiating element II has been shown comprising a rectangularsheet, it will be apparent that sheet elements having other thanrectangular shapes may be used without departing fromthe scope oftheinvention. For example, diamond-shaped,- triangular, elliptical or otherplane figures maydefine the edges of radiating element l I. I

The inductive stubs l9, 2| are provided to neutralize thereactivecomponentof the antenna impedance. The stubs I 9,,2l togetherwithelement ll effectively constitute sections of transmission linehaving plane conductors, which are short-circuited atone end by shortingbars 23, 25. In accordance with known transmission line theory, thelength of the stubs and their separation from element Il may be computedso as to 1 cause the studs to present an inductive reactance ofvsubstantiallyequal magnitude to the capacitive reactance of theradiating element ll, over a wide band of frequencies. Thus, means areprovided for maintaining a substantially nonreactive termination of theline 11 by the an- The invention described herein may be manuefacturedand used by or for the Government of the United States of America forgovernmentar purposes without the payment ofany royalties,

thereon or therefor.

What is claimed is: f 1. An antenna comprising a conductive sheet havinga length of substantially one-quarter of the operating wave -length and;g. width'whieh is a fraction less than unity of the operatingwavelength, a transmission line, and means for coupling the line to theconductive sheet comprising a tapered flat divergent conductor sectioninterposed between the line and the conductive sheet.

2. An antenna comprising a conductive sheet having a length ofsubstantially one-quarter of the operating wave-length, and a widthwhich is a fraction less than unity of the operating wavelength, atransmission line, and means for coupling the line to the conductivesheet comprising a tapered flat divergent conductor" section interposedbetween the line and the conductive sheet, and -a dielectric housingenclosing the conductive sheet.

3.1m combination, an antenna comprising a conductive sheet havinga'length of substantially one-quarter of the operating wavelength, and.a width which is a fraction les than unity of the operating wavelength,meansdefining an extended ground plane conductive supporting surface forthe antenna, a transmission line, and tapered fiat divergent conductormeans for coupling the line to the antenna; r i l 4; In combination anantenna comprising a conductive sheet having a lengthof substantiallyone-quarter of the operating wavelength, a finite thickness, and a widthwhich is substantially one-eighth of :the operating wavelength, acoaxial transmission line, having an inner conductor With-a diameterequal to the thickness of the conductive sheet, means defining anextended ground plane conductive supporting sure face for the antenna,and a taperedflat divergent section of the transmission Je-ineforaeffectingsa gradual transition between the widths of the iconductive sheet and thecross-sectionaldimensions of the line. 1 e

5. In combination an antenna -.comprising =a conductive sheet .having alength of substantially one-quarter of the operating wavelength and awidth which is substantially one-eighth .of the operating.;,wav:elength, .means defining an ex tended ground plane conductivesupporting ,=su r.-

{ace for :the antenna,'=a pair of conductive elements positionedparallel to the conductive sheet on opposite sides thereof and connected-:to the sheet intermediate the ends thereof, a coaxial transmissionline, and :taperedmonductor :means coupling the line to the conductivesheet.

6. An antenna comprising a conductivesheet having a length ofsubstantiallyone-quarterof the operating wavelength and a width which issubstantially one-eighth of said "Wavelength, and a pair of inductivetransmission line elements shorter than :the conductive sheetpositionedparallel to the sheet and conductively connected to l thesheet atone end of eachrelement.

wavelength, a pair of conductive elements shorter than the conductivesheet positioned parallel to the sheet and conductively connected to the.sheetat one end of each element, a transmission line, and taperedconductor means for coupling the line to the antenna.

,8. An antenna comprising a conductive sheet having a length ofsubstantially one-quarter of I the operating wavelength and a widthwhich is substantially one-eighth of said wavelength, a

pair of conductive elements shorter than the conductive sheet positionedparallel to the sheet and conductively connected to the sheet at one endof each element, a transmission line, and tapered conductor means forcoupling the line to the antenna, and means defining anextended groundplane conductive supporting surface for the antenna, the antenna and theline extending in opposite directions from the conductive surface.

9. An antenna comprising, a conductive sheet having a length ofsubstantially one-quarter of the operating wavelength, and a width whichis substantially one-eighth of the operating wavelength, means definingan extended ground plane conductive supporting surface for the antenna,a transmission line, a tapered planar conductive member coupling oneconductor of the transmission line with the conductive sheet, and a pairof divergent tapered flat planar conductive'members disposed on opposingsides of the planar conductive member connecting'a second conductor ofthe transmission line with the aforementioned means. 10. Anantennacomprising, a conductive sheet having a length of substantiallyone-quarter of the operating wavelength, a finite thickness, and a widthwhich is substantially one-eighth of the operating wavelength, meansdefining an extended ground plane conductive supporting surface for theantenna, a transmission line having at least a first conductor equal inthickness to the thickness of the conductive sheet and a second c0n--ductor, a tapered planar conductive member coupling the first conductorof the transmission line to the conductive sheet, and a pair ofdivergent tapered flat planar conductive members disposed on opposingsides of the planar conductive member connecting a second conductor ofthe transmission line with the aforementioned means.

JOHN T. BOLLJAHN.

REFERENCES "CITED The following references are of record in the file ofthis patent:

V v UNITED STATES PATENTS Number

